Clustering of Leafcutter Bee (Megachile lippiae) Damage is not Explained by Positive Feedback

• Published in: Western North American naturalist Vol. 85; no. 1; pp. 1 - 12
• Main Author: Luizzi, Victoria J.
• Format: Journal Article
• Language: English
• Published: Provo Western North American Naturalist 01.04.2025
• Subjects: Accumulation; Animal cognition; Bees; Clustering; Consumers; Cutting; Cuttings; Damage; Feedback; Foraging behavior; Leaves; Linings; Megachile; Megachile lippiae; Megachilidae; Nests; Positive feedback; Scleria mitis; Arizona
• ISSN: 1527-0904
• DOI: 10.3398/064.085.0101

Damage to leaves caused by animals is often distributed unequally, with few plants or individual leaves receiving the bulk of the damage. However, the mechanisms that generate these distributions are rarely understood. This is especially true for foliar damage caused by leafcutter bees (Megachile spp., Megachilidae), which use cut leaf discs to construct the linings of their nests. Leafcutter bee damage is highly clustered at the individual leaf level, but nothing is known about what is responsible for this pattern. I studied the leaf-cutting behavior of the leafcutter bee Megachile lippiae on cultivated roses (Rosa * hybrida) to understand whether the clustering of many cuts on individual leaves is due to positive feedback, with bees becoming more likely to cut a leaf solely because it has already been cut. This could occur if bees use social information (i.e., decisions previously made by other individuals) to decrease costs associated with leaf foraging. I identified a characteristic set of behaviors bees engage in when foraging for rose leaves. i then quantified which of these behaviors bees performed, and for how long, when the bees were on leaves that had and had not been previously cut to determine whether the presence of a cut in itself results in differences in bee behavior (e.g., decreasing evaluation time). Finally, I experimentally cut leaves, removing an ellipse of tissue similar in size, shape, and location to natural cuts, and compared the accumulation of cuts on these leaves to the accumulation of cuts on unmanipulated leaves and leaves that had been subject to non-leafcutter-like damage. I found that bees behaved similarly and spent similar amounts of time on cut and noncut leaves. in the cutting experiment, there was no difference in cut accumulation among the treatments, suggesting that the presence of a leafcutter-like cut on a leaf is not sufficient to induce additional cutting. This suggests that the clustering of leafcutter bee cuts on particular leaves is not explained sufficiently by a simple positive feedback mechanism, and instead must be driven in part by other factors. I propose several alternative causes for cut clustering that deserve further attention.